WASHINGTON — With a bill like a duck but teeth like a croc’s, a swanlike neck and killer claws, a new dinosaur species uncovered by scientists looks like something Dr. Seuss could have dreamed up.

It also had flippers like a penguin, and while it walked like an ostrich it could also swim. That’s the first time swimming ability has been shown for a two-legged, meat-eating dinosaur.

The tiny creature, only about 18 inches tall, roamed 75 million years ago in what is now Mongolia. Its full curled-up skeleton was found in a sandstone rock.

“It’s such a peculiar animal,” said Dennis Voeten, a paleontology researcher at Palacky University in the Czech Republic. “It combines different parts we knew from other groups into this one small animal.”

In a study released Wednesday by the journal Nature, Voeten and coauthors named it Halszkaraptor escuilliei or “Halszka” after the late Polish paleontologist Halszka Osmolska.

Its mashup body let it run and hunt on the ground and fish in fresh water, said study co-author Paul Tafforeau.

He’s a paleontologist at the ESRF , known as the European Synchrotron in Grenoble, France, a powerful X-ray generator where numerous tests were made on the fossil.

Even though the creature wasn’t dreamed up by Dr. Seuss, it got a blessing from a Dr. Sues.

Hans Sues, a paleontologist at the Smithsonian Institution who wasn’t part of the research, said it “shows again how amazingly diverse dinosaurs were.”